Video frames are typically compressed using different algorithms. These different algorithms for video frames are called picture types or frame types, and the three major picture types used in the different video algorithms are I-frames, P-frames and B-frames. I-frames are the least compressible but do not require other video frames to decode. P-frames can use data from previous I-frames to decompress and are more compressible than I-frames. B-frames can use both previous and forward frames for data reference to get the highest amount of data compression.
Set top boxes are typically designed to display multiple layers of images in the video output to display devices, such as, televisions, by providing one or more overlays in a main window. The term overlay may be defined as an image displayed over an image displayed in a main window of a display device. Examples of overlays include an Electronic Program Guide (EPG), closed captioning, Picture-in Picture (PIP), etc. Conventionally, set top boxes fully decode the video images in the main window, including the sections that are covered by overlays. The decoding process typically consumes a great deal of bandwidth and thus reductions in the bandwidth consumption are desirable.